Automated and semi-automated hematology analysis apparatus of the type employed for measuring a plurality of parameters of a whole blood sample have been in common use for many years. One of such systems is the subject of U.S. Pat. No. 3,549,994 and in using such systems, means have been provided for introducing whole blood samples into the system manually via an open-mouthed sample container which is held up to an aspirating tube or probe from which it is aspirated and thereby directed to a metering, transfer and delivery valve assembly of the type taught by U.S. Pat. No. 4,445,391. The said type of valve assembly meters the aspirated sample into precise volume aliquots and delivered with a predetermined volume of diluent to the testing means provided within the system.
Although numerous improvements have been made over the years to systems of the type concerned, for many years the method and means for introducing sample to the system have remained unchanged. Some advances have been made in sample handling such as taught in U.S. Pat. No. 4,609,017 in that sealed sample containers have been provided and handled by automatic and semiautomatic feed arrangements using holding racks and piercing needle means to combine sample mixing and aspiration enabling with a goal to minimize technician interaction and reducing the sample volume required. In such apparatus, the piercing needle is coupled by a fluid conduit line to the metering, transfer and delivery valve assembly. In some of these systems, the piercing needle means is required to be physically located within a very short distance from the valve assembly. In such systems, the aspirated blood volume is required to be large enough to fill the needle, the connecting fluid conduit and the valve assembly. This aspirated blood volume, of course is continuous along such route and hence is much greated than required to fill the valve assembly.
In respect of systems wherein manual aspiration means are provided, again the volume of aspirated blood sample is much larger than necessary to enable the valve assembly to provide the required aliquot portions. Conservation of sample has been and remains an important and as yet unrealized goal to the extent theoretically possible. Even where the sample aspiration probe is directly secured to the valve assembly, the volume aspirated into the probe has been far greater than the theoretical minimum, the excess passing through the valve assembly and to waste. Thus whether the aspiration station, whether it involves a piercing needle semi-automatic or automatic mode or a manual aspiration probe mode, is remote from the valve assembly or closely adjacent the valve assembly, the resultant aspirated sample volume is greater than actually required for the determinations sought to be obtained.
Another deterrent to the efficient aspiration of whole blood sample is the structural complexity required where the aspiration station and the valve assembly are positioned closely adjacent one another. If it were possible to obtain minimum volume units of sample at a location remote from the valve assembly and transport said units to the valve assembly with preservation of their integrity so that only the volume required to establish the necessary fluid body for segmentation within the valve assembly to provide the aliquot portions is drawn, the volume of blood sample to be aspirated would be manifestly reduced.
Thus it would be desirous to provide an blood sample aspiration method which would enable the reduction of the volume of whole blood sample aspirated to an amount at least close to the theoretical minimum required to isolate the required aliquot portions of the sample necessary to obtain the desired parameters of said sample. Also sought is a method for locating the aspiration station remote from the valve assembly yet assuring continuity of sample and maintaining the integrity thereof. Further, another advantage sought is an inexpensive method to position the body of blood sample so that it just fills the flow path therefor within the sampling valve assembly. The method sought by the art to solve the above problems likewise should improve the ease of cleaning the aspiration lines from the probe tip through the blood sampling valve without needing the backflushing conventionally available.